Approximately five to ten percent of patients with cystic fibrosis are believed to have the disease because cells lining their airways are not capable of synthesizing a protein called the cystic fibrosis transmembrane conductance regulator (CFTR) due to premature stop mutations. We have discovered that in some cases it may be possible to stimulate cells to make the normal protein by treating them with the same antibiotics which cystic fibrosis patients routinely receive as part of their therapy. Aminoglycoside antibiotics (Tobramycin, Gentamicin, Amikacin) are routinely given to cystic fibrosis patients for the treatment of lung infections. The purpose of this study is to determine whether these same antibiotics might also help a subgroup of cystic fibrosis patients by allowing their lung cells to produce a normal CFTR protein. To date, 7 patients have completed the study. We intend to study 20 additional patients in the future.